1. Field of the Invention
The invention relates to an automatic document feeder which is carried on a main body of an apparatus such as a copying machine, and particularly to an automatic document feeder capable of placing a pair of original documents side by side on a contact glass.
2. Description of the Related Art
In Japanese Laid Open Patent No. 63-93462 and Japanese Laid Open Patent No. 63-285563, a conventional automatic document feeder is disclosed. The automatic document feeder has an ordinary mode for feeding and transporting documents one by one, and a mode for serially placing an earlier fed document and the next document side by side on the contact glass (hereinafter referred to as a 2-in-1 mode). The automatic document feeder includes a document feeding part which comprises a separating member and a pair of pull-out rollers, and a document transporting part in the form of a transporting belt. The document feeding part separates and feeds documents one by one from a bundle of documents. The document transporting part transports the documents fed by the document feeding part to an exposing position on a contact glass sized to accommodate a pair of documents, where the main body of the apparatus performs an exposing operation. The document transporting part then discharges the documents from the exposing position after the exposing operations are carried out.
When the 2-in-1 mode is selected, the document feeding part separates and feeds a document (a first document) from a bundle of documents and the document transporting part transports the first document downward. The document transporting part then halts transportation of the first document after the trailing edge of the first document passes the pull-out rollers, and thereafter the document transporting part reverses the first document such that the first document contacts the downstream side of the pull-out rollers.
Next, the document feeding part separates and feeds the next document (the second document) and makes the leading edge of the second document contact the upstream side of the pull-out rollers, whereby the first and second documents are positioned. The document feeding part and the document transporting part are then driven and the first and second document are placed side by side at the exposing position on the contact glass.
The main body of the apparatus exposes the first and second documents and copies the document images of the first and second documents on one paper sheet (so-called 2-in-1 copy).
In this type of the automatic document feeder, as the trailing edge of the first document and the leading edge of the second document are adjusted at the downstream and upstream sides of the pull-out rollers, the leading edge of the second document can not directly contact with the trailing edge of the first document. In other words, the nip portion of the pair of pull-out rollers prevents the leading edge of the second document from directly contacting with the leading edge of the first document. As a result of the space between the trailing edge of the first document and the leading edge of the second document even when the first and second documents are transported to the exposing position on the contact glass, a part of the document image may extend beyond the exposing position and thus would not be properly copied onto a paper sheet.
Japanese Laid Open Patent 2-225241, proposes an automatic document feeder for overcoming the aforementioned problems. In this arrangement, after feeding and transporting a first document onto a contact glass, a transporting belt reverses the first document to abut the first document against a positioning member (a document scale), which is provided on an upstream side of the contact glass, whereby the first document is positioned in place. The second document is fed until a space between a leading edge of the second document and a trailing edge of the first document moves a predetermined distance by a feeding part, and the first and second documents are fed and transported downward together until the trailing edge of the second document passes over the positioning member. Further, the transporting belt is reversed by an amount corresponding to a total of a distance between the positioning member and the trailing edge of the second document, and a distance between the first and second documents, such that the trailing edge of the second document abuts against the positioning member. In addition, the trailing edge of the first document abuts against the leading edge of the second document and the space between the first and second documents is eliminated. However, to eliminate a space between the first and second documents, the transporting belt reverses twice. The reversing operation wastes time and causes a significant increase in noise (since the noise level increases at the point when the feeding is reversed) in order to serially place a pair of documents in this type of automatic document feeder.